Radical elements are now a threat to the survival of Pakistan, prompting Pakistani military leaders to recognize that more aggressive efforts are needed to get the elements under control, Director of National Intelligence Mike McConnell said yesterday in testimony before the Senate Select Committee on Intelligence.

"In the last year, the number of terrorist attacks and deaths were greater than the past six years combined," McConnell said in an unusually strong warning about Pakistan's political problems. "What's happened is Pakistan has now recognized that this is an existential threat to their very survival."

Pakistani leaders, he said, are "starting a process to be more aggressive in getting control of the situation." The elements include al-Qaeda and Taliban members who for years were nurtured by Pakistani military and intelligence officials, prompting U.S. lawmakers and others to question the sincerity of the government's effort.

At the same hearing, focused on threats to U.S. interests around the globe, CIA Director Michael V. Hayden publicly confirmed for the first time that the agency's interrogators had used a simulated drowning technique known as waterboarding on a total of three al-Qaeda detainees in 2002 and 2003.

After the hearing, Hayden told reporters that the information obtained from those detainees amounted to a quarter of all the human intelligence the CIA gained about the terrorist organization between 2002 and 2006.

"We would not have done it if it were not that valuable," Hayden said after he and other intelligence community leaders testified. The agency has been under pressure to justify its use of the technique because military officials, lawmakers, human rights experts and international lawyers have called it torture banned by U.S. laws and treaties.

Hayden confirmed previous reports that waterboarding was used against Zayn al-Abidin Muhammed Hussein, known as Abu Zubaida; Abd al-Rahim al-Nashiri; and Khalid Sheik Mohammed, considered as the mastermind of the 9/11 attacks. "We used it against these three detainees because of the circumstances at the time," Hayden said, noting: "There was the belief that additional catastrophic attacks against the homeland were inevitable. And we had limited knowledge about al-Qaeda and its workings."

A specially appointed federal prosecutor has opened a probe into the CIA's destruction of videotapes showing Nashiri being interrogated and Zubaida being waterboarded. Typically, the latter involves strapping a person on a board, with his head tilted downward, while water is poured onto cloth or cellophane covering the face.

A senior intelligence official at the hearing yesterday said that the CIA officers and contractors who conducted interrogations involving waterboarding were told it was legal at the time, but he added that "the legal landscape has changed." The official, who spoke on the condition of anonymity, said the Justice Department's investigation is "potentially chilling" for agency personnel.

FBI Director Robert S. Mueller III, when asked at the hearing whether the FBI used the same interrogation techniques employed by the CIA, replied: "It has been our policy not to use coercive techniques." He added that this policy reflects the fact that FBI questioning is mostly done within the United States and often involves U.S. citizens.

On another controversial issue, McConnell said that, in retrospect, "I probably would have changed a thing or two" in the public presentation two months ago of a National Intelligence Estimate that concluded that Iran had stopped work on the design of a nuclear weapon. The estimate appeared to conflict with Bush administration rhetoric and undermined Washington's effort to win support for tough sanctions against Iran.

McConnell said yesterday that the halt in the design work was the "least important part" of the program and "the only thing halted." He said Iran had continued its production of fissile material, although he noted that it faces "significant technical problems" operating centrifuges. He also disclosed differences within the community about when Tehran could get enough highly enriched uranium for a weapon, with some saying 2009, others 2010 to 2015, but all recognizing the possibility that it could not come "until after 2015."

Meanwhile, McConnell and Attorney General Michael B. Mukasey wrote Senate Majority Leader Harry M. Reid (D-Nev.) yesterday to register opposition to several proposed Democratic amendments to a new surveillance bill. The measures are likely to come to a vote today.

One of the controversial amendments would strike a provision granting telecommunications companies immunity from dozens of lawsuits alleging violations of privacy because of the firms' cooperation with a warrantless government surveillance program initiated after the attacks of Sept. 11, 2001.

Another would require the attorney general and the director of national intelligence to certify that any surveillance the government conducts "is limited to communications" involving specific individual targets reasonably believed to be outside the United States.

A third would require that a special court approve surveillance if a "significant purpose" of that effort is to acquire the communications of a person reasonably believed to be inside the United States.

The latter two are meant to prevent unauthorized government spying on U.S. citizens and residents. But McConnell and Mukasey complained that they would create "unacceptable operational uncertainties and problems," hindering intelligence-gathering when a foreign terrorist overseas is calling into the United States.